Performance of a foundation pit supported by bored piles and steel struts: A case study

Abstract Retaining structures with bored piles and temporary inclined steel struts are suitable for the reinforcement of underground projects located in urban areas of high-density development as they are convenient for use in earth excavations and their use leads to considerable savings in time and cost. However, few data are available on foundation pits supported by bored piles and inclined steel struts. This paper presents a case study to investigate the behavior of a large-scale foundation pit supported by bored piles and inclined steel struts, in which the movement of the foundation pit and the displacement of the retaining structure are reported. The measured results along the length of the foundation pit were found to be smaller than those along the width (with a difference of approximately 13.5–30.0%), including the vertical and lateral displacement of the foundation pit, as well as the lateral displacement of the bored piles. The lateral displacement at the top of the bored piles, δ h , was 0.2–0.5% of the excavation depth, H e . The lateral displacement of the bored piles decreased with the decreasing distance from the corner (with a difference of approximately 50%), which demonstrated the corner effect on the movement of the bored piles. Based on the measured results of this field case, it was found that the maximum settlement and the lateral displacement were located at the cross section through the center of the west side of the foundation pit. In order to predict the distribution of settlement at the surface and the basal heave at this section, plane-strain finite element analyses were conducted to estimate the location where the maximum settlement occurred at the surface of the foundation pit. The difference between the numerical results and the measurements was found to be in the range of 2.6–33.0%, which validates the numerical model with some reasonable accuracy. The numerical results show that the maximum surface settlement occurred at a distance of 0.6 H e away from the top of the foundation, whereas the settlement at the bottom of the foundation was almost uniform at the final construction stage (e.g., 25 mm).